Continuous stream ink jet printing uses a pressurized ink source to supply ink to one or more nozzles to produce a continuous stream of ink from each of the nozzles. Stimulation devices, such as heaters positioned around the nozzle, stimulate the streams of ink to break up into drops with either relatively large volumes or relatively small volumes. These drops are then directed by one of several systems including, for example, electrostatic deflection or gas flow deflection devices.
In printheads that include gas flow deflection systems, the drop deflecting gas flow is produced at least in part by a gas, typically air, drawn laterally across the drop trajectories into a negative gas flow duct as a result of vacuum applied to the duct. Drops of a predetermined small volume are deflected more than drops of a predetermined large volume. This allows for the small drops to be deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) where they are either recycled or discarded. The large drops are allowed to strike the print medium. Alternatively, the small drops may be allowed to strike the print medium while the larger drops are collected in the ink capturing mechanism
It has been determined that while small drops are deflected by the lateral airflow more than large drops, not all small drops follow the same trajectory. Some of these drops can be deflected sufficiently by the air flow such that they enter the gas flow duct, causing ink puddles to form. Ink puddles in the gas flow duct can also be formed during startup and shutdown of the printhead, caused by ink dripping off the upper wall of the gas flow duct and landing on the lower wall of the gas flow duct. Additionally, ink puddles can be formed due to a crooked jet which causes ink to be directed into the gas flow duct. Ink from the puddles of ink in the gas flow duct can be dragged by the gas flow up into the vacuum source that is attached to the gas flow duct, possibly damaging the vacuum source. If the ink puddles remain close to the entrance to the duct, these puddles can affect the uniformity of the air flow across the width of the jet array. Ink puddles can induce oscillations in the gas flow that can produce a modulation in the print drop trajectories that adversely affect print quality.
U.S. Pat. No. 8,091,991 described a drain for removing such ink from the negative gas flow duct and also a method for cleaning the negative gas flow duct. It has been determined that under certain operating conditions fine satellite drops or mist can be formed. The fine satellite drops, having much less volume than either the large or small drops, are deflected by the gas flow much more than the large or small drops. The deflection of these satellite drops can be sufficient to cause them to be ingested into the negative gas flow duct, and for them to remain air borne past the duct drain. The satellite drops can collide with the walls of the gas flow duct downstream of the duct drain where they form a deposit on the walls of the gas flow duct. These deposits can build up so that they interfere with the normal operation of the printhead.
Accordingly, a need exists to remove such deposits from the interior of the negative gas flow duct, and in particular to remove such deposits from portions of the negative gas flow duct downstream of the duct drain, to reduce or even prevent a degradation of the operation of the printhead.